The present invention relates generally to an implementation of the connectivity algorithm, and more particularly to a novel hardware architecture that allows the connectivity algorithm to be implemented efficiently on every pixel in an image in real time.
It is discussed in said allowed application that in the forward-looking infrared (FLIR) imaging of a non-uniform scene such as terrain, point targets whose temperature is substantially higher or lower than that of the background (e.g. aircraft at long range) are often not detected by the target detection algorithms conventionally used in FLIR imaging. Conventional target detection algorithms can also falsely mark many background clutter features as targets. Such target detection algorithms include leading-edge-trailing-edge detection and least-mean-squared (LMS) filtering. One-dimensional LMS filters can produce false target indications on edges of background objects, as is the case for leading-edge-trailing-edge detection, and even the use of two orthogonal one-dimensional LMS filters can still produce false target indications on corners. It has been found to be necessary, in order to isolate point targets for a clear display, to determine the spatial extent and spatial connections of an object of interest in real time. This is a difficult computational feat.
The inventors are aware of several references either generally dealing with the problem or a similar one, which references are identified as follows:
U.S. Pat. No. 4,005,415, concerns an automated radar data processing system comprised of signal processing circuitry and programmed general purpose digital computer apparatus performing detection, classification and tracking functions with respect to all targets within the field of view of the radar. The signal processing circuitry includes an adaptive video processor which receives the raw radar video signals and which derives a threshold from the noise, clutter, or electronic countermeasures signals in the immediate vicinity of the target and passes only those incoming signals which satisfy the detection criteria in terms of signal to noise ratio and extent. The signal processing circuitry is interactive with target track data derived and stored in the computer apparatus, so that the specific signal processing applied to any target by the adaptive video processor is optimized in accordance with the track status of that target.
U.S. Pat. No. 4,233,387. This invention concerns a device that examines a two dimensional quantized picture to determine whether any objects are closer together than a set minimum distance. The quantized picture has incremental areas assigned values of 0 or 1 corresponding to the presence or absence of an object. An array of interconnected logical cells identifies the presence of a separate object in the picture. The dimensions of the array correspond to the acceptable minimum distance between objects. The described device contains only basic digital logic components and processes picture information without the use of a computer program.
U.S. Pat. No. 4,489,388, concerns a plot generator for selecting angle, range and target azimuth extent data produced for targets and stored in a register. The generator comprises a video processor for generating the data on the reception of sensor signal data. This references describes a system based on dividing the radar coverage into a number of range-azimuth zones and on establishing a standard number of plots to be processed for each zone, which standard number depends on the position of the zone in respect of the target approach routes, and allowing for a maximum number of plots to be processed by the central processor each antenna revolution.
U.S. Pat. No. 4,593,406. The invention described in this reference involves a computerized method and point location system apparatus for ascertaining the center of a primitive or fundamental object whose shape and approximate location are known. The technique involves obtaining an image of the object, selecting a trial center, and generating a locus of points having a predetermined relationship with the center. Such a locus of points could include a circle. The number of points overlying the object in each quadrant is obtained and the counts of these points per quadrant are compared. From this comparison, error signals are provided to adjust the relative location of the trial center. This is repeated until the trial center overlies the geometric center within the predefined accuracy limits.
U.S. Pat. No. 4,685,143. This invention relates to recognition of images by the construction and analysis of edge maps in an automatic image processing and recognition scheme. In order to overcome the disadvantage of the usual requirement of the storage of large amounts of information, the techniques described in this reference computes an edge spectrum from the edge map. The edge spectrum contains useful information in a form even more condensed than the edge map from which it is derived and is processed by any of several feature detectors to determine whether, for instance, the edge map contains mutually orthogonal edges or other structural details useful in identifying the image.
U.S. Pat. No. 4,736,439. This invention pertains to image transformation or pre-recognition processing using adaptive quantization based on a local average. The image preprocessing technique described in this reference involves image preprocessing by median filtration in which the median value of one or more rows of pixels of a digitized image represented by a matrix, as might result from a raster scan, is subtracted from the values of individual pixels to filter low and high frequency noise.
U.S. Pat. No. 4,742,557, concerns a method and a system for extracting relevant character information from fields of scanning data which contain unwanted background information and noise that is picked up in the scanning process. The system of this reference uses not only a gray level comparisons, but also the comparison of topological features (i.e. geometrical distribution of character pixels), to adaptively adjust a threshold for each individual check which threshold determines the cut-off from consideration of character information.
In contradistinction to the techniques described in and utilized by the above-noted prior art references, the invention described in said allowed application utilizes the connectivity algorithm, where the imaging electronics examine the pixel intensities of pixels forming a closed path around the centroid of a potential target object. The examining electronics require the pixels' intensities to differ in a predetermined manner from the centroid's intensity in order to be part of the path. If such a path can be drawn before any pixel of the path exceeds a predetermined distance from the centroid, the potential target object is identified as a real target and can be displayed as such.
In the past, the connectivity algorithm could only be performed on real time video data by processing a pre-filtered subset of pixels with a general purpose processor. This approach required a considerable amount of both hardware and software. Targets that did not pass the pre-filter could not be detected. The hardware architecture and implementations of the present invention eliminate these problems and provide some features that enhance the basic connectivity algorithm.